It is known in the art to provide a mechanical governor for internal combustion engines having means for controlling engine idle speed as well as for preventing engine operation above a preset maximum speed or range of speeds. One type of governor used for such purposes has centrifugal flyweights which act through a linkage against an idle speed spring and, upon its full compression, on a high speed spring which controls maximum engine speed. Between the preset idle and maximum speeds, the fuel input is controlled manually by the operator of the engine or vehicle, with the speed controlling functions of the governor coming into play only to prevent the engine from operating below its idle speed or above its preset maximum speed.
In certain engine applications, particularly vehicle applications in which governors of the above mentioned and other types have been used, devices have been provided either within or external to the governors to modulate the maximum engine fuel input at speeds intermediate the idle and maximum speeds. One purpose of such arrangements is to prevent overfueling of the engine cylinders at low engine speeds in order to control emissions of smoke, oxides of nitrogen or other undesirable exhaust products. While some such arrangements have been useful, it is believed that none have accomplished their desired purposes in the manner of the present invention.